Triplex antenna

ABSTRACT

An antenna system for operation in the UHF and VHF band comprising at least three individually excited tubular dipole antennas vertically oriented in an in-line configuration inside of a tubular radome and being spaced approximately one wavelength apart. Each tubular radiation element is excited by means of a Gamma Match feed (DC grounded) for protection against lightning and destructive effects from high level electromagnetic pulses. A coaxial sleeve approximately a quarter wavelength long is additionally mounted exteriorly of and is associated with each tubular radiating element inside of the radome for broadbanding the feed-point impedance of the respective dipole antennas.

United States Patent 91 Czerwinski 1 Aug. 12, 1975 Primary Examiner-EliLieberman Attorney, Agent, or FirmNathan Edelberg; Robert P. Gibson;Arthur L. Bowers [5 7 ABSTRACT An antenna system for operation in theUHF and VHF band comprising at least three individually excited tubulardipole antennas vertically oriented in an in-line configuration insideof a tubular radome and being spaced approximately one wavelength apart.Each tubular radiation element is excited by means of a Gamma Match feed(DC grounded) for protection against lightning and destructive effectsfrom high level electromagnetic pulses. A coaxial sleeve approximately aquarter wavelength long is additionally mounted exteriorly of and isassociated with each tubular radiating element inside of the radome forbroadbanding the feed-point impedance of the respective dipole antennas.

14 Claims, 3 Drawing Figures TRIPLEX ANTENNA The invention describedherein may be manufactured and used by or for the Government forgovernmental purposes without the payment of any royalties thereon ortherefor.

BACKGROUND OF THE INVENTION The present invention relates generally toantenna systems for radiating and intercepting electromagnetic energyand more particularly to a vertical dipole antenna array for permittingsimultaneous operation of a plurality of radio apparatus in the samefrequency band.

Tactical military aircraft control centrals are known to operate up tothree radio sets (transceivers) simultaneously on the same UHF(220-400MH2) and/or VHF (1 -1 SOMHz) frequency bands. Presently, theseunits utilize a separate but identical antenna for each of the radiotransceivers in both the transmit and receive modes. These antennas,however, are mounted in a cluster laterally spaced with respect to oneanother, having a separation of one wavelength which for an operatingfrequency of 300MHz is in the order of 40 inches. Experience has shown,however, that when one antenna is operating in the transmit mode,sufficient energy is coupled into the other antenna(s) to render its(their) respective receiver(s) inoperable due to high level ofcross-talk and receiver desensitization. Therefore, due to thislimitation, it is current practice to use only one transmission link ata time. Such practice, however, has been found to be unsatisfactory whenair traffic becomes relatively dense due to the fact that more than onelink is necessary in order to insure safety against collision betweenincoming and outgoing aircrafts.

Additionally, it is well known that electrical isolation between twodipole antennas fed from separate radio signal sources is significantlygreater when the dipoles are mounted one above the other on the sameaxis as opposed to being arranged in a broadside relationship with thesame relative spacing between feed points. The following references areknown to constitute prior art arrangements of such vertical in-lineantenna systems:

U.S. Pat. No. 2,115,761, A. D. Blumlein;

U.S. Pat. No. 2,158,376, W. Mosher, et al.; and

U.S. Pat. No. 2,425,585, H. A. Wheeler.

SUMMARY Briefly, the subject invention comprises at least a three bayvertically stacked dipole antenna assembly having individually excitedtubular dipole radiating elements axially aligned along a commonvertical central axis and being respectively fed from separate radioapparatus operable in the same frequency band and being fed by what isgenerally referred to as a Gamma Match by coaxial cables fed through arelatively small diameter metallic tubular support conduit running upinside of the radiating elements. A tubular broadbanding element havinga length shorter than the respective radiating element is arrangedcoaxially with and exteriorally of the respective tubular dipoleradiating element, being held in place by the inner surface of a tubularradome. Each of the dipole radiating elements are separated bysubstantially one wavelength and the tubular support conduit containingthe coaxial feeds are adapted to include lossy coating and ferrite ringson the conduits outer surface for limiting unwanted circulating currentsand to increase the desired electrical isolation between bays.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view illustrative ofthe preferred embodiment of the subject invention;

FIG. 2 is an enlarged fragmentary view of a longitudinal cross sectionof the embodiment shown in FIG. I, being illustrative of one bay of theantenna array; and

FIG. 3 is a still further fragmentary view of the embodiment shown inFIG. 1, being further illustrative of the bay shown in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT An antenna is a conductor soconstructed as to either radiate or collect electromagnetic energy or todo both. A transmitting antenna converts electrical energy from a sourceinto electromagnetic waves called radio waves which radiate away fromthe antenna at speeds near the velocity oflight. A receiving antenna onthe other hand converts electromagnetic waves which it intercepts intoelectrical energy and applies this energy to radio receiver apparatusfor interpretation. Some antennas such as that forming the subjectinvention are adapted to serve both functions being coupled totransceiver apparatus which is adapted to both send and receivecommunication signals.

A halfwave dipole antenna is not only a fundamental element of anantenna system, it is particularly adapted for communications for use inapplications above ZMHZ (2 X I()'Hertz). Basically. the halfwave dipoleantenna is comprised of two quarterwave conductors linearly aligned andhaving the inner extremities thereof excited by an RF generator. Suchapparatus is well known to those skilled in the art and is welldocumented in the literature.

The subject invention is directed to the problem of operating aplurality, for example, three sets of radio apparatus simultaneously onthe same frequency band while being in relatively close proximity to oneanother but sufficiently decoupled to permit operation of each withoutinterference from the others. Referring now to the drawings and moreparticularly to FIG. 1, the antenna system comprising the subjectinvention includes, for purposes of illustration, three tubular halfwavedipole radiation elements l0, l2 and 14 mounted on a common supportconduit 16 in the fo.'m of a grounded metal pipe or the like by means ofrespective metal support plates or grounding discs, not shown. Thedipole elements 10, 12 and 14 are axially aligned with the metal supportconduit 16 thus having a common central axis which is verticallyoriented. The spacing between adjacent dipole elements 10, I2 and 14 isin the order of one wavelength (A) of a predetermined center frequencyof operation, which includes both the UHF band (220-400MH2) as well asthe VHF band (ll5l50MHz).

The three bay configuration shown in FIG. I includes tubular dipoleantenna elements which have substantially the same overall physicaldimensions inasmuch as they are adapted to operate in combination withrespective radio apparatus operating in the same frequency band.Therefore only one of the three dipole elements ie. the middle element12 is shown in FIGS. 2 and 3 for the purposes of further illustratingthe details of the subject invention. For operation in the region of300MHz, the dipole elements 10, 12 and 14 consist of aluminum tubingtypically having an outer diameter in the order of 2 inches and a length(M2) in the order of 20 inches. Referring now to FIG. 2, the supportconduit 16 is of a relatively smaller diameter grounded metal pipe andis hollow so as to act as a passageway for the respective coaxial dipoleelement feedlines 24, 26 and 28, which respectively terminate in threecoaxial connectors 30, 32 and 34 mounted on a first or lower base plate36. These coaxial connectors are adapted to be coupled to separateaforementioned radio apparatus, now shown. A fourth connector 38 is alsolocated in the base plate 30 for the connection of AC line potentialthereto from a source not shown. An AC line cord 40 coupled to theconnector 38 is adapted to travel up through the conduit 16 to the topof the entire antenna assembly for lighting one or more hazard lights 42located on a sub-assembly including a support member 44 having a globe46 attached thereto as shownin FIG. 1. The purpose of the hazard lights42 is due to the fact that the overall height of the antenna system isin the order of 25-30 feet for operation in the VHF band and in theorder of l-20 feet for operation in the UHF band and since the primaryuse of such apparatus is for aircraft control, being located in closeproximity to an airstrip.

Continuing with the structural details, the base plate 36 containing thecoax connectors 30, 32 and 34 as well as the AC connector 38 is attachedto the lower portion of a metal sleeve 48 which has a second base plate50 attached to the upper portion thereof. The base plate 50 includes amounting hole at the center to which the lower end of the supportconduit 16 is secured. A radome 52 comprising a tubular structure formedof fiberglass or the like is fitted to the inside surface of the sleeve48, coming to rest on the base plate 50 as shown in FIG. 2. Thesub-assembly for the hazard lights 42 and including the support member44 is adapted to fit over the other end of the radome 52. Additionally,a third or upper base plate 54 is fitted inside the upper portion of theradome 52 and includes a hole at its center whereupon the top portion ofthe conduit 16 is inserted therein and secured. Thus what is obtained isa relatively tall. thin, tubular type assembly adapted to include atleast three dipole tubular radiators l0, l2 and 14, spaced approximatelyone wavelength apart inside of the radome 52 and being attached to theinner support conduit pipe 16 by means of respective metallic spacers,for example element 18 shown in FIGS. 2 and 3. Dielectric spacers and 22are additionally included near both ends of the radiating dipole elementfor providing added support.

Each of the dipole elements 10, 12 and 14, moreover, has a respectiveimpedance broadband element 56, 58 and 60 associated with it which isshown comprising a quarter wavelength \/4 section of thin wall aluminumtubing or aluminum foil of relatively larger diameter than the elementsthemselves and being fitted and held stationary inside of the radome 52by the fact that the outer diameter of the sections 56, 58 and 60 ismade equal to the inner diameter of the radome 5 2. This is shown ingreater detail in FIG. 2 with respect to element 58. The broadbandingsections 56, 58 and 60, moreover, are arranged such that they aresubstantially midway between the lengths of the respective radiatorsthus providing a symmetrical arrangement.

Since the excitation connection of the respective coaxial cable to eachdipole element is the same for all three bays, only one will beconsidered in detail. Referring now to FIG. 3 and the bay including thedipole element 12, the braid or outer conductor 62 of the coaxial cable26 is grounded to the metal support disc 18 after being fed out ofa holeor port 64 in the conduit 16 near the disc 18. This ground connection isshown for example by means ofa set screw 66. It should be noted,however, that any type of electrical connection can be made such as bysoldering and could be to the conduit 16 itself near the port 64 whendesired. The inner conductor 68 of the coax 26 is fed across the innerdiameter and through a hole or opening 70 in the dipole element 12 andconnected to the outer surface thereof by means of another set screw 72.The location of the connection of the inner conductor 68 to the outerwall surface of the dipole element 12 is significant, being at a pointof minimum VSWR in the coaxial feed cable 26. This comprises a distanceL 0.05 away from the grounding point of the outer conductor 62 i.e. atthe location of the metal support disc 18. At 300MHz, this distance istypically 2 inches. This type of feed to a dipole antenna is generallyreferred to as a Gamma Match. Such a feed connection is selected becauseit results in a DC grounded antenna desirable for protection againstlightning and destructive effects from highlevel electromagnetic pulses(EMP).

Undesired antenna current which would normally be coupled to the surfaceof the support pipe 16 and having a tendency to limit the level ofelectrical isolation obtainable between adjacent dipole elements 10, 12and 14 is dissipated by coating the outside surface of the conduit 16with a lossy ferrite material. Additionally, lossy ferrite rings shownschematically by reference numerals 82 and 84 in FIG. 1 are affixed tothe outer surface of the pipe 16 intermediate the lower and middledipole elements 10 and 12 and the middle and upper dipole elements 12and 14, respectively.

Thus what has been shown and described is a multiple dipole array in theform of Iight weight one-piece adapted to operate a plurality of radiosets simultaneously within the same frequency band while beingelectrically isolated from one another. Each dipole moreover is capableof broadband operation with a VSWR less than 3:] by virtue of thebroadbanding effects of elements 56, 58 and 60 and is adapted to providean omnidirectional radiation pattern. By proper phasing of the feedbetween each dipole, high gain operation as a single radiation source iseasily obtainable. Since all members are grounded to DC, automaticprotection against lightning is obtained.

Having thus described what is at present considered to be the preferredembodiment of the subject invention, I claim as my invention:

1. A broadband antenna system for a plurality of radio apparatus adaptedto operate simultaneously in the same frequency band, comprising incombination:

a generally vertically oriented electrically conductive and groundedsupport conduit of predetermined length;

a respective plurality of in-line tubular dipole radiating elements, onefor each of said plural radio apparatus. axially mounted on said supportconduit. the inner surface of said tubular radiating elements beinggrounded to said conduit substantially midway along their respectivelengths;

a port in the sidewall of said support conduit at the location of eachof said radiating element;

a respective coaxial cable, having an inner and outer conductor.coupling each radiating element to a respective radio apparatus of saidplurality of radio apparatus, running through support conduit and out ofa respective port, said outer conductor being electrically grounded inthe vicinity of said port;

each said tubular radiating element having an opening to the outer wallsurface thereof wherein the inner conductor of the respective coaxialcable passes therethrough and is electrically connected to said outersurface; and

respective impedance broadbanding means for each of said dipoleradiating elements disposed exteriorally of each of said radiatingelements. 7

2. The antenna system as defined by claim 1 wherein each said respectivebroadbanding means comprises quarter wavelength tubular elementscoaxially disposed outside of the respective tubular radiating elementand positioned intermediate the length of said tubular radiatingelement.

3. The antenna system as defined by claim 2 wherein said coaxial tubularbroadbanding element is disposed substantially mid-way along the lengthof the respective tubular radiating element.

4. The antenna system as defined by claim 3 and additionally including atubular radome coaxially oriented with respect to said plurality oftubular radiating elements and their respective tubular broadbandingelements, said radome having an inner surface which is adapted to holdthe broadbanding tubular elements in position relative to the respectiveradiating elements.

5. The antenna system as defined by claim 4 wherein said support conduitcomprises a tubular member of a relatively small cross sectionaldimension with respect to said tubular radiating elements and having theouter surface coated with lossy material for providing electricalisolation between adjacent radiating elements.

6. The antenna system as defined by claim 5 and additionally includingat least one ring of lossy material disposed on the outer surface ofsaid tubular member located intermediate said plurality of radiatingelements for providing additional electrical isolation between adjacentradiating elements.

7. The antenna system as defined by claim 1 wherein said opening in eachsaid tubular member is located approximately 0.05 wavelength of apredetermined operating frequency distance away from the point along thelength of said radiating element wherein the inner surface of saidelement is grounded to said support conduit.

8. The antenna system as defined by claim 1 and additionally includingrespective electrically conductive support and grounding means attachingeach tubular radiating element to said support conduit, said means beingdisposed normal to the common central axis of said support conduit andsaid plurality of tubular radiating elements.

9. The antenna system as defined by claim 8 wherein the outer conductorof each coaxial cable is electrically connected to said support andgrounding means.

10. The antenna system as defined by claim 1 and additionally includingmeans located at the upper end of said support conduit for mounting atleast one hazard light thereon. and electrical conductor means foroperating said hazard light running through said support conduit.

11. The antenna system as defined by claim 1 wherein said plurality ofradiating elements comprises at least three substantially identicaltubular radiating elements having a mutual separation of approximatelyone wavelength of a predetermined operating frequency.

12. The antenna system as defined by claim 1 and additionally includinga mounting sleeve and a first base plate attached to the lower portionthereof. said plate including a respective plurality of coaxial cableconnectors mounted thereon and being respectively connected to eachcoaxial cable, a second base plate attached to the upper portion of saidsleeve. said support conduit being mounted on said second base plate.

13. The antenna system as defined by claim 12 and additionally includinga tubular radome fitted to said mounting sleeve.

14. The antenna system as defined by claim 13 wherein said impedancebroadbanding means comprises quarter wavelength tubular sections. andwherein said support member, said plurality of tubular radiatingelements and respective tubular broadbanding elements as well as saidtubular radome are circular in cross section.

1. A broadband antenna system for a plurality of radio apparatus adaptedto operate simultaneously in the same frequency band, comprising incombination: a generally vertically oriented electrically conductive andgrounded support conduit of predetermined length; a respective pluralityof in-line tubular dipole radiating elements, one for each of saidplural radio apparatus, axially mounted on said support conduit, theinner surface of said tubular radiating elements being grounded to saidconduit substantially mid-way along their respective lengths; a port inthe sidewall of said support conduit at the location of each of saidradiating element; a respective coaxial cable, having an inner and outerconductor, coupling each radiating element to a respective radioapparatus of said plurality of radio apparatus, running through supportconduit and out of a respective port, said outer conductor beingelectrically grounded in the vicinity of said port; each said tubularradiating element having an opening to the outer wall surface thereofwherein the inner conductor of the respective coaxial cable passestherethrough and is electrically connected to said outer surface; andrespective impedance broadbanding means for each of said dipoleradiating elements disposed exteriorally of each of said radiatingelements.
 2. The antenna system as defined by claim 1 wherein each saidrespective broadbanding means comprises quarter wavelength tubularelements coaxially disposed outside of the respective tubular radiatingelement and positioned intermediate the length of said tubular radiatingelement.
 3. The antenna system as defined by claim 2 wherein saidcoaxiAl tubular broadbanding element is disposed substantially mid-wayalong the length of the respective tubular radiating element.
 4. Theantenna system as defined by claim 3 and additionally including atubular radome coaxially oriented with respect to said plurality oftubular radiating elements and their respective tubular broadbandingelements, said radome having an inner surface which is adapted to holdthe broadbanding tubular elements in position relative to the respectiveradiating elements.
 5. The antenna system as defined by claim 4 whereinsaid support conduit comprises a tubular member of a relatively smallcross sectional dimension with respect to said tubular radiatingelements and having the outer surface coated with lossy material forproviding electrical isolation between adjacent radiating elements. 6.The antenna system as defined by claim 5 and additionally including atleast one ring of lossy material disposed on the outer surface of saidtubular member located intermediate said plurality of radiating elementsfor providing additional electrical isolation between adjacent radiatingelements.
 7. The antenna system as defined by claim 1 wherein saidopening in each said tubular member is located approximately 0.05wavelength of a predetermined operating frequency distance away from thepoint along the length of said radiating element wherein the innersurface of said element is grounded to said support conduit.
 8. Theantenna system as defined by claim 1 and additionally includingrespective electrically conductive support and grounding means attachingeach tubular radiating element to said support conduit, said means beingdisposed normal to the common central axis of said support conduit andsaid plurality of tubular radiating elements.
 9. The antenna system asdefined by claim 8 wherein the outer conductor of each coaxial cable iselectrically connected to said support and grounding means.
 10. Theantenna system as defined by claim 1 and additionally including meanslocated at the upper end of said support conduit for mounting at leastone hazard light thereon, and electrical conductor means for operatingsaid hazard light running through said support conduit.
 11. The antennasystem as defined by claim 1 wherein said plurality of radiatingelements comprises at least three substantially identical tubularradiating elements having a mutual separation of approximately onewavelength of a predetermined operating frequency.
 12. The antennasystem as defined by claim 1 and additionally including a mountingsleeve and a first base plate attached to the lower portion thereof,said plate including a respective plurality of coaxial cable connectorsmounted thereon and being respectively connected to each coaxial cable,a second base plate attached to the upper portion of said sleeve, saidsupport conduit being mounted on said second base plate.
 13. The antennasystem as defined by claim 12 and additionally including a tubularradome fitted to said mounting sleeve.
 14. The antenna system as definedby claim 13 wherein said impedance broadbanding means comprises quarterwavelength tubular sections, and wherein said support member, saidplurality of tubular radiating elements and respective tubularbroadbanding elements as well as said tubular radome are circular incross section.